What is RISC?
A reduced instruction set computer is a computer which only uses simple commands that can be divided into several instructions which achieve low-level operation within a single CLOCK cycle, as its name proposes “Reduced Instruction Set”.
Example: Apple iPod and Nintendo DS etc.
What is CISC?
A complex instruction set computer is a computer where single instructions can perform numerous low-level operations like a load from memory, an arithmetic operation, and a memory store or are accomplished by multi-step processes or addressing modes in single instructions, as its name proposes “Complex Instruction Set ”.
Example:IBM 370/168, VAX 11/780, Intel 80486 etc.
Difference Between CISC and RISC
The main difference between RISC and CISC is in the number of computing cycles each of their instructions take. The difference the number of cycles is based on the complexity and the goal of their instructions.
| Architectural Characterstics | Complex Instruction Set Computer(CISC) | Reduced Instruction Set Computer(RISC) |
|---|---|---|
| Instruction size and format | Large set of instructions with variable formats (16-64 bits per instruction). | Small set of instructions with fixed format (32 bit). |
| Data transfer | Memory to memory. | Register to register. |
| CPU control | Most micro coded using control memory (ROM) but modern CISC use hardwired control. | Mostly hardwired without control memory. |
| Instruction type | Not register based instructions. | Register based instructions. |
| Memory access | More memory access. | Less memory access. |
| Clocks | Includes multi-clocks. | Includes single clock. |
| Instruction nature | Instructions are complex. | Instructions are reduced and simple. |
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